Mercury is the only metal that is in liqid form at room temperature. Caesium, Gallim and Rubidium are also metals that are in liquid form but at slightly high temperature than the room temperature.
MAC - Media Access Control, address is a globally unique identifier assigned to network devices, and therefore it is often referred to as hardware or physical address.
MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format.